Ferroelectric materials have become well known since the discovery of Rochelle salt for their properties of spontaneous polarization and hysteresis. See the International Dictionary of Physics and Electronics, D. Van Nostrand Company Inc., Princeton (1956) at pg. 331. Other ferroelectrics including barium titanate have also become familiar subjects of research.
However, the application of the properties of ferroelectric materials to millimeter wavelength devices and radar systems is largely uncharted scientific terrain.
At MM wavelengths, standard microwave practice is hampered by the small dimensions of the working components, such as waveguides and resonant structures. Furthermore, there is a considerable lack of suitable materials from which to make the components. Even beyond this, the manufacturing precision demanded by the small dimensions of the components, makes their construction difficult and expensive. Ferrite phase shifters used at other frequencies are unsuitable, and alternative materials are generally not available.
Ferroelectric materials are accordingly of particular interest, because certain of their dielectric properties change under the influence of an electric field. In particular, an "electro-optic" effect can be produced by the application of a suitable electric field.
As is well known, ferroelectric materials are substances having a non-zero electric dipole moment in the absence of an applied electric field. They are frequently regarded as spontaneously polarized materials for this reason. Many of their properties are analogous to those of ferromagnetic materials, although the molecular mechanism involved has been shown to be different. Nonetheless, the division of the spontaneous polarization into distinct domains is an example of a property exhibited by both ferromagnetic and ferroelectric materials.
A ferroelectric medium has the property that its propagation constants can be changed by applying a sufficiently intense electric field along a suitable direction. This phenomenon is known as the electro-optic effect. Ferroelectric media are unique since they are capable of linear electro-optic activity in contrast to more familiar media wherein the electro-optic activity is typically quadratic. This linear activity, defined as a linear dependence of the refractive index on the applied electric field, is a consequence of the domain structure of the ferroelectric material.
Accordingly, it is an object of this invention to establish a device for continuously focussing and defocussing a millimeter radiation passing through a ferroelectric medium by electrical means.
It is an object of this invention to develop a millimeter wavelength focussing and defocussing device for use in radar signal control operation, amplitude modification and beamsplitting.
It is an object of the invention to develop a ferroelectric millimeter wavelength device for microwave radar application at the millimeter wavelength range, which is reversibly and continuously controllable over a range of focal distances.
It is a further object of the instant invention to produce a millimeter wavelength ferroelectric focusser and defocusser effective for processing microwave signals in a radar system.